I feel this discussion keeps repeating the same way over and again. Aye, if they turn up on our doorstep, the effects on us will be entirely down to them. I doubt we'd be enslaved. Human slaves would be useless compared to sufficiently advanced machines. I doubt we'd be food. If they're sophisticated enough to get here they've probably cracked food production in whatever forms they need it. If they can breathe our air and want Earth for expansion of their own civilization, they'll probably want rid of us. I'd suggest releasing some kind of probe swarm in the atmosphere to seek us out and eradicate us. We'd probably never see it coming and would have no defence. Little point in them modifying the planet to their biology as the most valuable thing Earth has going for it is its biosphere. But if they can't live in our atmosphere or modify themselves to do so, and Earth really does suit their needs in every other way, their job is even easier. Giant atmospheric processors land on Earth to change our atmosphere, and we'd all die, and they can start replacing our biosphere with lifeforms taken from their own.
So, yes, if they turn up here, we would probably stop being so materialistic, and generally so alive.